Even before you’ve seen her, you know her. Jane (Katherine Heigl) is the perennial sad singleton, lonely but eternally hopeful. She’s in love with her boss (Ed Burns), who treats her like the world’s most lovingly cared-for doormat, and she has been an eager and devoted bridesmaid 27 times, with her leftover dresses — in all their fruit-hued, puffy-sashed, prom-discard plumage — lined up in the closet to prove it. You already know him, too. Kevin (James Marsden) is the jaunty solo male, unlassoed by love, who somehow manages to pen the tenderhearted ”Commitments” column in the Sunday wedding section of the New York Journal. Staring him in the eye, she asks: Does he really feel all those warm, sincere, special-day sentiments? Or is he just a cynic spooning out ”romantic crap” for women like her?

That’s a question you could well ask the people who concocted 27 Dresses: screenwriter Aline Brosh McKenna, who previously wrote the hit screen adaptation of The Devil Wears Prada, and director Anne Fletcher, a veteran choreographer who turned filmmaker with Step Up (2006). It’s not that their movie is cynical; it’s that all the chick-flick trappings — the fashion, the wedding chitchat, the masochistic one-way crush — drive the story rather than the other way around. 27 Dresses is a movie geared to a pitch of high matrimonial-princess fever. It’s white-lace porn for girls of every age, and the way that it revelsin that get-me-to-the-altar mood, to the point of making anyone who isn’t getting married feel like a loser, is the picture’s key selling point.

McKenna and Fletcher, at moments, give good romantic fluff, and they offer a few tweaks — though not enough — of the poshly retro-traditional multibillion-dollar wedding industry. There are also winning performers on screen, like Katherine Heigl, who knows how to glow right through her professional-woman composure. She soft-pedals her sexiness with just the right touch of exasperation. Heigl, amid the friendly mishegoss of Knocked Up, signified as a nearly generic shiksa goddess, but really, she’s a far more exotic actress than that. Her face is all ovals and darting eyes — she’s got some of the nervous, high-strung sensuality of the young Kathleen Turner — and she makes Jane a live presence, even if it’s a bit much to ask us to believe that a woman this attractive could be this nerdishly self-sacrificing a sop.

And yet, merely by writing that line, I have revealed how completely removed I am from the target audience for this movie. As far as they’re concerned, if 27 Dresses were ”better,” it probably wouldn’t be as good. It wouldn’t have that guilty-pleasure, how-I-learned-to-stop-worrying-and-love-the-cheese frisson that has become the defining spirit of the 21st-century chick flick. McKenna’s script melts together a couple of cookie-cutter plots. In the first, Jane’s dim-bulb, duplicitous, baby-doll sister, the platinum bimbo Tess (Malin Akerman), snares the boss that Jane has spent years adoringly stepping and fetching for. Will Tess now get to enjoy the perfect Central Park Boathouse nuptials — in Mom’s old wedding dress! — that Jane always longed for? Meanwhile, Jane sets off a few damp, sputtering sparks with Kevin, who is planning to write a splashy Sunday feature on her existence as the ultimate bridesmaid. But she, poor dear, has no clue that he’s even doing a story! James Marsden, so foppishly funny as the fairy-kingdom prince in Enchanted,lathers on the charm here like too much aftershave. His Kevin is so gauntly male-modelish and smug, he’s like the screwball hero as gigolo.

It’s hard to imagine a set of complications more routine, but the way that this tiered cake of a farce has been staged, you can practically lick the white frosting off of the plot. Even the satire of the wedding industry plays like a backhanded endorsement of it. There is, of course, a trying-on-clothes montage, though this one has a rare dash of wit: It’s Jane modeling all her bridesmaid’s dresses (which, according to the film, are meant to look bad, so that they don’t show up the bride), as the movie flashes back to the weddings in which she wore them. There’s also an intentionally cringe-worthy (though maybe not this much) duet between Jane and Kevin, who take refuge at a bar following an auto mishap. Drunk on whiskey, the two sing along with ”Bennie and the Jets,” getting down with their bad selves in their most impassioned, white-person fervor, which inspires the entire bar to join in. Love means never having to say you’re sorry for acting like an idiot. Or for tying yourself in knots in order to tie the knot. C+